This invention relates to a single very light tubular building element for the construction of reinforced concrete intermediate floors/ceilings and roofs. The single building element provides the formwork for the casting in place of the structural concrete and also provides for a high quality finished ceiling at the same time. It is intended for simple installation without heavy equipment into building parts. A series of members are often intended to form an exposed surface when used as a floor or ceiling.
A series of members are constructed and often arranged to be the primary means of containing and supporting a panel or slab of concrete as it cures. An interconnected series of members, according to the present invention, also form a continuous mortar impervious formwork for a concrete slab, and presents an attractive permanently exposed ceiling surface.
There have been many suggestions for use of either or both temporary or permanent form members to construct building parts of concrete. These form members can be temporary in nature since they are removed after concrete cures, or can be contained in concrete as permanent parts.
For example:
U.S. Pat. No. 4,742,660 teaches a modular building system of extruded hollow thermoplastic structural components of rectilinear cross-section. These members are made of a special thermoplastic mixture said to resist the elements and are characterized by a fire-resistant outer skin. The concrete is poured inside the thermoplastic components which have internal apertures through which the concrete can flow from one member to another member in a group when they are joined as a wall panel, for example. When the members are to be used in construction of a roof, concrete cannot be used, and metal inserts are called for to assist in stiffening.
U.S. Pat. No. 5,729,944 discloses the use of thermoplastic structural components as permanent formwork. The forms can be used in a series to construct various structures. Concrete is poured inside the thermoplastic components which have internal apertures through which the concrete can flow from one member to another member when they are joined as a wall panel.
U.S. Pat. No. 5,397,096 is illustrative of conventional concrete forming techniques to manufacture a ribbed, reinforced concrete slab. The forming system utilizes concrete displacement pans supported on temporary framework. The patent discloses the problem of concrete leaking out of joints. The leaking material normally is without aggregate, and is sometimes referred to as mortar. When the concrete slab or slab cures, workers must remove the hardened mortar with a chisel, or the like, providing an unsatisfactory surface finish. The bottom surface is neither planar nor finished. The patent suggests the use of additional members to forestall the leakage of mortar.
U.S. Pat. Nos. 4,557,031 and 5,216,863 are illustrative of other expedients to join extruded plastic form members for use in containing concrete inside. The members are normally a part of the cured concrete structure or building component.
U.S. Pat. No. 5,535,565 is illustrative of a containment including a plurality of panels that are interconnected by connector columns and fused together by the passing of electrical current through conductors received within such elements at their points of intersection. The panels are interconnected by sliding one adjacent panel over another panel. A gasket is interposed between a pair of panels to create a watertight environment.
U.S. Pat. No. 5,535,565 is illustrative of a highly sound insulating clay tile for the construction of floors that has an outer substantially parallelepiped shape with symmetrical, laterally projecting portions that act as shoulders for the support of each tile by prefabricated reinforced concrete floor beams.
While the field of reinforced concrete formwork is well-developed, there is still the need for a relatively inexpensive easy-to-use system to form ribbed-concrete slabs with structural formwork components. The system should not be as labor intensive as prior art arrangements. It should use components that are lightweight and yet will control elastic deformation such as is often encountered when steel and aluminum alloy formwork is used to make such ribbed structures. Moreover, each element should be easily aligned with an adjacent member, the alignment means providing an impermeable alignment between adjacent members. Thus, eliminating the need of additional members (e.g. gaskets) or fusing of the adjacent members to accomplish impermeability.
Further, the members making up the formwork should not be filled with concrete, to create the slab. Similarly, the members should include an easy device for placement of reinforcement bars without the need of manual tying or securing of the reinforcement bars together.
It is also desirable to have the ability to incorporate the formwork into the slab and have it serve as an impervious formwork base, eliminating cumbersome cleaning during construction and leakage afterward, and saving the common need of a costly waterproofing membrane over the slab. The formwork should serve for the casting in place of the structural concrete and also should provide for a high quality finished ceiling at the same time, eliminating the need to plaster and otherwise enhance the aesthetic appeal of the ceiling. Finally, the formwork should facilitate hung ceiling installations and also be easily penetrable to hold threaded screws and the like.
There is provided an elongated tubular member arranged to be interconnected in a series. Each member is constructed of extruded thermoplastic material, is relatively thin walled, and light in weight. In a preferred embodiment, it will weigh less than four pounds per square foot, i.e., the individual members weigh about 2 pounds per linear foot, so that a 5 meter long member weighs about 32 pounds and can be handled by only one laborer without need of special equipment. It is intended to be incorporated in structural, reinforced ribbed concrete slabs used in roofs and floors.
The members serve as a continuous mortar impervious formwork on the bottom of a poured concrete slab while it is curing. It thus avoids the leakage of concrete mortar through formwork joints during concrete pouring and cure time which leakage can result in honeycomb void defects that cause the structure to be prone to possible future corrosion of steel reinforcement contained in the concrete slab. Such corrosion is often difficult and costly to repair.
The formwork permanently serves as the bottom of the slab. It is an impervious barrier of the type essential for roof construction and thus eliminates the need for an exterior waterproofing membrane. The formwork has transverse, flexural strength and stiffness sufficient to resist vertical and lateral construction loads without significant deformation. It can bear the weight and pressure of wet concrete, needing but few transverse intermediate temporary supports directly under the hollow elements which make up the formwork. For example, a line of 4xc3x974 wooden purlines, spaced about five feet apart over 4xc3x974 wooden shores, also spaced about five feet apart, or equivalent simple systems of metal purlines and shores can be used.
The members are generally formed of a PVC (polyvinyl chloride) alloy conforming with Uniform Building Code (UBC). Any UBC conforming extrudable and light weight similar material of equal or better strength and durability will be suitable. This general type of theremoplastic is lightweight and easily formed by extrusion with many integral convenient features, but has lower modulus of elasticity (stiffness) than most other construction materials. For example, the modulus of elasticity of steel is more than sixty times more than in thermoplastic and the modulus of elasticity for aluminum is more than thirty times more than in thermoplastic.
The center section is like the hat crown and the wings are like a hat brim. A member is defined by a top and a parallel bottom wall interconnected by parallel side walls which are substantially perpendicular to the top and bottom walls. There is an internal generally horizontal wall between the enclosing side walls. Above that internal horizontal wall and limited by the top and side walls is formed a closed rectangular box-like conduit when viewed from an end. In that rectangular space, it is easy to install a band of fiberglass mat to improve thermal insulation of the concrete slab, if desired. Below that internal horizontal wall and connecting it with the bottom and side walls, there is a web of three shorter longitudinal internal walls. One of them is a longitudinal vertical wall extending from the center of the horizontal internal wall (at a central intersection) to the center of the bottom wall. In one embodiment, the other two web walls are symmetrical, sloped down and outward from the center intersection. The side wings taper from a relatively thick area adjacent the side wall to the narrowest area at the end where there is a finger or groove. The sloped walls, side wall bottom wall, and bottom left and right intersections between the bottom wall and side walls are thickened in the area where the wings join the side walls thereby forming an area better able to absorb bending stress which reduces consequent deformation from the side wings when wet concrete is poured above them.
In a second embodiment, the two sloped walls extend symmetrically, are sloped down and outward from a first set of two symmetrical points very close to the center intersection of the horizontal internal wall, through the side walls, and rest at points on the wings near the left and right intersections between the bottom wall and the side walls. Because the sloped walls rest on the wings, they act as tensors and increase the stiffness of each wing sufficient to counter deformation caused by vertical forces acting downward on the top of the wings. In this embodiment, there is no need to taper the thickness of all members connected at the bottom right and left intersections as there is when using the embodiment described above.
There are wing-like webs extending outwardly from each side of each member, having a lower surface, which is substantially on the same plane with the outside lower surface of the bottom wall. The outermost end of one wing has an upwardly extending finger or tongue; and the outermost end of the second wing has a groove like an inverted U, arranged upwardly with the opening facing down. The finger and groove serve as an alignment means. The groove-ending wing fits easily above the tongue-ending wing in a lapping relationship between adjacent members when such members are laid up in a series prepared to receive wet concrete. Since each member has always both wing ending types, for proper lap matching, all members for a formwork deck shall be laid with the tongue wing ending on the same side; that side corresponding with the direction in which the installation proceeds.
The construction technique of the present invention facilitates hung ceiling installations to form a plenum through which heating and air conditioning pipes or ducts are passed.
Further, the construction facilitates the accurate arrangement of steel reinforcing bars because of the unique construction of parts. The invention permits the construction of ribbed reinforced concrete slabs with about one-half the weight of concrete, which might otherwise be required, which slabs are both resistant and stiff.
It is an object of the invention to provide lightweight, thermoplastic structural formwork members constructed and arranged to be interconnected in a series to serve as formwork for ribbed concrete slabs.
Another object of the invention is to provide lightweight, inexpensive, and easy to install structural members for use in constructing ribbed concrete slabs.
Another object of the invention is to provide formwork for ribbed concrete slabs that forms a continuous impervious structure, eliminating the needs for exterior waterproofing membranes when used in roof construction.
It is another object of the invention to provide formwork which has the longitudinal and transverse flexural strength and stiffness sufficient to resist the weight of the wet and vertical and lateral construction loads, yet needing few transverse intermediate temporary supports while the concrete cures.
It is another object of the invention to provide ribbed concrete formwork having a pleasant appearing exposed surface capable of being used as a finished ceiling with regular longitudinal features or embossing which can be formed during the extrusion process at no extra cost.
Another object of the invention is to facilitate hung ceiling installation in commercial and institutional buildings where it is necessary to have a plenum for heating and air-conditioning pipes and duct work above the ceiling. The formwork provides outward indicia or other markings indicative of areas in which hanger means for the ducts and pipes may be located with assurance of sufficient holding strength of easily penetrated material, for example, to screw in hangers for the hung ceiling, ducts, and pipes.
Another object of the invention is to facilitate installation of thermal insulation for the ribbed slab.
It is yet another object of the invention to facilitate the accurate and easy installation of steel reinforcing bars and/or splice bars in association with the formwork before pouring of the concrete.
Yet another object of the invention is to provide for construction of ribbed reinforced concrete slabs using about one-half the normal weight and volume of concrete as compared to conventional forming techniques.
These and other objects, features, and advantages of the present invention will be more clearly understood and appreciated by review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims.